Traditionally, telephony applications have been built within isolated, vertical platforms—i.e., self-contained boxes, each performing a fixed set of functions. Such applications have been specifically designed for each particular vendor, hence providing little opportunity for enhancements and addition of functions. Generally, custom modifications to traditional telephony applications required a substantial financial investment, as well as time to implement, test, and deploy. Therefore, technological and market developments could not be easily accommodated.
More recently, however, service providers have recognized that differentiated services drive markets more so than price competition models. Accordingly, they have offered groups of services, sometimes closely bundled, in order to attract new subscribers. Unfortunately, as mentioned above, traditional telephony applications do not typically provide custom functions, and do not lend themselves to integration. Attempts have been made in the past to provide open application environments that facilitate the development of new applications for providing custom services. However, such open application environments frequently require that service providers write their custom applications entirely. This has proven to require more investment than the service provider could justify.